This invention relates to traffic control equipment used to monitor the states of traffic signal head control signals for proper operation. More particularly, this invention relates to a malfunction management unit which monitors for the absence of any activated traffic signal head control signals in a given channel.
Traffic signal heads are commonly used to regulate the flow of vehicular and pedestrian traffic. A typical traffic signal head is provided with red, yellow, and green A.C. operated light sources, and the operation of these light sources is under the control of a unit termed a controller assembly. For safety reasons, the traffic control industry has long used equipment to monitor the states of the electrical power signals generated by the controller assembly and used to operate the traffic signal head light sources for proper operation. Under the TS-1 standard, this equipment is called a conflict management unit (CMU); under the later TS-2 standard, this equipment is called a malfunction management unit (MMU).
A controller assembly and an MMU are typically configured together in one of two configurations-Type 16 and Type 12. In either configuration, the traffic control signals from the controller assembly to the signal heads in a controlled intersection are typically grouped into channels, with the signals for a given phase assigned to the same channel. In a Type 16 configuration, there are a total of sixteen channels, each consisting of three 120 volt A.C. outputs:Green/walk, Yellow, and Red/Don't Walk. In a Type 12 configuration there are a total of twelve channels, each consisting of four 120 volt A.C. outputs: Green, Yellow, Walk, and Red.
One of the tests customarily applied to the control signals in each channel is termed the Red Fail test. This test checks whether at least one of the traffic light control signals in a channel is active. If not, all the lights controlling that phase of the intersection are dark and the phase is uncontrolled. When this condition occurs, the MMU generates a fault signal and the traffic signals are forced into a flashing mode of operation, overriding the normal mode of operation.
Although the Red Fail test is widely used, this standard test is inaccurate and not suitable for some intersection arrangements. For example, in some overlaps and some protected/permitted applications it may be required that the lights in one channel all be dark while another channel's lights are active. Under the normal Red Fail test, the absence of an active light in the one channel would trigger a Red Fail fault unless the MMU were programmed to inactivate the Red Fail test.